US Patent application published as US Patent Publication No. 2006/0033154 and U.S. patent application Ser. No. 11/890,849 both assigned to the assignee of the present application and incorporated by reference, disclose power MOSFETs having deep source field electrodes.
Integrated Schottky diodes are available in state of the art trench MOSFETs with breakdown voltages in the range of 20-30V. These Schottky diodes take advantage of the trench structure to form a Trench MOS Barrier Schottky (TMBS) structure that provides low leakage and low Vf compared to planar Schottky diodes. Current trench technologies for devices with higher breakdown voltages (40-300) may not be suitable for an integrated TMBS type device due to higher leakage and Vf.
According to one aspect of the present invention, a high performance Schottky diode is integrated with a MOSFET having deep source field electrodes. Advantageously, the deep source field electrodes of the MOSFET allow an integrated Schottky with low reverse leakage and low Vf to be formed when the mesa width is appropriately chosen.
Simulations have shown that a Schottky diode in a device according to the present invention offers both lower leakage and Vf than a Schottky diode that could be created with a traditional trench process flow. Moreover, such a device may exhibit significantly lower Vf than a MOSFET integrated with a pn junction diode which allows a Schottky diode according to the present invention to operate at higher current levels.
According to one aspect of the present invention, in order to form an integrated Schottky in any of the previously disclosed process flows for a MOSFET with deep source field electrodes, two additional masks and a barrier metal process are employed. The first mask blocks the channel implant from the Schottky region of the device, and the second mask blocks the high conductivity contact region implant from the Schottky region.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.